This invention relates to a rotary damper which is disposed between a device main body and a rotary member rotatably supported on the device main body such as a main body of a toilet and its cover and adapted to prevent high-peed rotation of the rotary member in at least one direction, thereby rotating the rotary member at a reduced speed.
As a conventional rotary damper of this type, there is one, for example, which is disclosed in Japanese Patent Application Laid-Open No. H10-311359. This rotary damper includes a cylindrical casing having a closed bottom portion, a rotor fitted to an open side end portion of the casing such that the rotor is rotatable but non-movable in the axial direction, a piston disposed between the rotor and the bottom portion within the casing such that the piston is movable in the axial direction but non-rotatable, and a coiled spring (biasing means) for urging the piston against the rotor. The mating surfaces of the piston and rotor are each provided with a cam surface. Owing to this cam surface, when the rotor is rotated in one direction, the piston is moved from the second chamber side to the first chamber side. When the rotor is rotated in the other direction, the piston is moved from the first chamber side to the second chamber side by the coiled spring. Between the first chamber and the second chamber, there are defined a communication path capable of flowing a viscous fluid filled in each chamber almost without any resistance and an orifice (resistance path) capable of flowing the viscous fluid with a large resistance. The communication path is provided with a stop valve for opening/closing the path. This stop valve is arranged such that the valve is opened when the viscous fluid in the first chamber is flowed into the second chamber and the valve is closed when the fluid is flowed from the second chamber into the first chamber, for example.
In the rotary damper thus construction, when the piston is moved from the second chamber side to the first chamber side by the rotor which is rotated in one direction, the viscous fluid in the first chamber is going to flow into the second chamber. However, since the stop valve closes the communication path at that time, the viscous fluid in the first chamber is flowed into the second chamber through the orifice. As a result, high speed movement of the piston towards the first chamber side is prohibited, and hence, high speed rotation of the rotor is prohibited. On the contrary, when the piston is moved from the first chamber side to the second chamber side by the rotor which is rotated in the other direction, the viscous fluid in the second chamber is flowed into the first chamber. Since the stop valve opens the communication path at that time, the viscous fluid in the second chamber is flowed into the first chamber through the communication path almost without any resistance. Thus, the rotor can rotate at a high speed.
In case the conventional rotary damper is used in a toilet, a casing is non-rotatably connected to a toilet main body and the rotor is non-rotatably connected to a toilet cover, for example. In this case, the direction of rotation where high speed rotation of the rotor is prohibited is brought into alignment with the direction of closing rotation of the toilet cover. By installing the rotary damper in this way, when the toilet cover is to be closed, speed of rotation of the toilet cover is retrained to a low speed so that the toilet cover is prevented from hitting the toilet main body at a high speed, and when the toilet cover is to be opened, the cover can be rotated at a high speed.
When the rotor is rotated in the other direction (direction of rotation where high speed rotation is allowed), the piston is moved from the first chamber side to the second chamber side by the biasing force of the coiled spring. At that time, if the rotor is rotating at a low speed, the piston is moved to the second chamber side while maintaining a contacting state of the rotor against the cam surface. However, in case the rotor is rotated at a high speed in the other direction, high speed movement of the piston is prohibited by viscous resistance of the viscous fluid existing between an inner peripheral surface of the cylinder and an outer peripheral surface of the piston. As a result, the piston is occasionally spaced apart from the cam surface of the rotor nevertheless the piston is biased towards the rotor side by the coiled spring. When the rotor is rotated in one direction with the piston spaced apart from the rotor, the rotor can rotate without any resistance until the cam surface of the rotor comes into contact with the piston. For this reason, if a hand should be spaced apart from the toilet cover during the time the toilet cover is rotating in the opening direction at a high speed, for example, the toilet cover would be rotated in the closing direction at a high speed with such an inconvenient result that the toilet cover hits the toilet main body.
The present invention has been accomplished in order to solve the above-mentioned problem. The feature of the present invention resides in a rotary damper including a casing having a receiving hole, a rotor fitted to the receiving hole such that the rotor is non-movable in an axial direction thereof but rotatable, a piston inserted into the receiving hole between the rotor and a bottom portion of the receiving hole such that the piston is movable in the axial direction thereof but non-rotatable, and for defining the inside of the receiving hole into a first chamber on the bottom portion side and a second chamber on the rotor side, and viscous fluid filled in the first and second chambers, a cam mechanism for allowing movement of the piston from the second chamber side to the first chamber side when the rotor is rotated in one direction and for allowing movement from the first chamber side to the second chamber side when the rotor is rotated in the other direction being disposed between the rotor and the piston, wherein a cam member is disposed within the first chamber such that the cam member is non-movable in the axial direction of the receiving hole but rotatable, the cam member is non-rotatably connected to the rotor, a second cam mechanism for allowing movement of the piston from the second chamber side to the first chamber side by the cam mechanism when the rotor is rotated in one direction and for allowing movement of the piston from the first chamber side to the second chamber side when the rotor is rotated in the other direction is disposed between the rotor and the piston, and amounts of movement of the piston corresponding to rotation of the rotor by the second cam mechanism and the cam mechanism are set to be equal.
In this case, it is preferred that there are provided a communication path for flowing the viscous fluid without any resistance and a resistance path for flowing the viscous fluid with a predetermined value of resistance, between the first chamber and the second chamber, and a stop valve for opening the communication path when the viscous fluid flows in one direction within the communication path and for closing the communication path when the viscous fluid flows in the other direction within the communication path is disposed at the communication path. It is also preferred that the piston has a through hole formed in a central area thereof and extending in an axial direction thereof, and the rotor and the cam member are non-rotatably connected to each other through a connection shaft rotatably inserted into the through hole.
It is preferred that an adjustment member for adjusting a flow path area of the resistance path is disposed at the resistance path such that the adjustment member can be operated from outside. It is also preferred that the piston has a through hole formed in a central area thereof and extending therethrough in an axial direction thereof, and the rotor and the cam member are non-rotatably connected to each other through a connection shaft rotatably inserted into the through hole. It is also preferred that the resistance path includes a first hole extending through a central area of the cam member in an axial direction thereof, a second hole extending through a central area of the connection shaft in an axial direction thereof, and a lateral hole extending from the second hole to an outer peripheral surface of the connection shaft facing the second chamber, an insertion hole is formed in a central area of the rotor in such a manner as to extend therethrough in an axial direction thereof, and the adjustment member is inserted at least into the second hole from an external opening portion of the insertion hole.
It is preferred that the rotary damper further comprises inlet paths communicating with the first chamber or the second chamber from outside, and wherein the inlet paths are provided, in the form of a seal, with an amount adjusting member, whose insertion amount into the inlet paths can be operated from outside. It is also preferred that the piston has a through hole formed in a central area thereof and extending therethrough in an axial direction thereof, and the rotor and the cam member are non-rotatably connected to each other through a connection shaft rotatably inserted into the through hole. It is also preferred that the inlet paths includes a first hole extending through a central area of the cam member in an axial direction thereof, a second hole extending through a central area of the connection shaft in an axial direction thereof, and an insertion hole extending through a central area of the rotor in an axial direction thereof, and the amount adjusting member is inserted into the inlet path from an external opening portion of the insertion hole.